During most of this century, glaucoma was defined as a blinding eye disease caused by an increased pressure within the eye. This pressure damaged the inner eye tissues leading to the loss of visual field. Science believed that if intraocular pressure (IOP) was lowered to a level under 21 mm on the Mercury Scale, the progression of the disease could be stopped. However, there are many cases where glaucoma occurs with IOP under 21 mm/Mercury, therefore, the level of IOP is not the only factor in producing this disease. New scientific technologies allow us to look more at the back of the eye and evaluate glaucoma from a circulatory, metabolic and hematological angle, therefore, being better able to determine the cause of the disease.
In order to be able to see, light enters through the comea and the lens; penetrates the back of the eye through the retina; passes the ganglion cells and bipolar cells; then goes down to the outer plexiform layers through the synaptic vesicle, the inner fiber, the nucleus, the outer fibers, the terminal bars, the cilium and finally reaches the photoreceptors which can be considered the instant film processing of the visual signal. After the light has been processed in the photoreceptor disks, it passes back through the cilium, the ellipsoid, myoid, Mueller cells, outer fiber, nucleus, inner fiber, synaptic vesicle, the other plexiform layer, inner nuclear layer, the bipolar cells, the inner plexiform layer, finally reaching the ganglion cells where it is processed into an axon signal. After it reaches the ganglion cells, the signal is transported through the optic nerve fibers to the brain where it is assessed and compounded by brain function and sent back to the eye in order to form the visual picture. It is believed that the uninterrupted signal carried in the optic nerve fibers is the most crucial aspect in the prevention of blindness. Glaucoma is seen as the progressive loss of optic nerve axons which leads to an interrupted signal flow, therefore, the result is visual field damage which leads over longer periods of time to blindness.
It has now been found that drugs in the class of .beta.-adrenergic blocking agents (.beta.-blockers) when administered intraocularly can maintain and improve the health of the optic nerve. .beta.-blockers include such drugs as timolol, cartelol, levobunolol, betaxolol, atenolol, metoprolol, nadolol, pindolol, propanolol, labetalol and the like. Timolol, (S)-1-(t-butylamino)-3-[(4-morpholino-1,2,5-thiadiazol-3-yl)-oxy]-2-propan ol and the other .beta.-blockers have been used primarily for the treatment of glaucoma. They act by inhibiting the aqueous humor production and therefore lowering intraocular pressure. Research during the last decade indicates that the health of the optic nerve is crucial to prevent the loss of the visual field.